You can get a job working for someone at an hourly rate. He might pay you $30 an hour. You do the job MANY times and get paid ONCE. If you need to make more money, you have to ask for a raise. He may say no. You may get laid off or fired.
You can also freelance, and charge $10 for custom keyword research. This is the same hourly rate as the job, but you do the job ONCE and get paid ONCE. (You can also do the job MANY times and get paid MANY times. Same thing.) If you need to make more money, you simply raise your prices. Nobody can stop you, and there will still be clients willing to pay.
Or... you can do keyword research when and how you want, pack it up as a "done for you" product, and sell it for $5. You do the job ONCE and get paid MANY times.
It's not hard to figure out which of these stands the greatest chance of making you rich, now, is it?
Whatever you do, however you get paid for it, this is your real job: turn it into WORK ONCE, GET PAID MANY TIMES. If you can't make something you do work this way, stop doing it. If you don't do anything that can work this way, go find something that does and start doing it.